The medical profession has long recognized the therapeutic impact of heat applied to tissue within the body. It is known that heating tissue can alter its physical properties (e.g., thermal necrosis, thermal denaturation, coagulation, shrinkage, or vaporization). The therapeutic effect of heat ranges in temperature from approximately 37.degree. C. (normothermic or body temperature) to hundreds of degrees Centigrade and depends on durations of exposure from fractions of a second to hours.
Not all tissue responds to temperature in the same way. For example, the temperature required to kill a malignant cell is known to be lower than that tolerated by most healthy cells. Thus, it is possible to use heat as a differential treatment for malignant disease. Similarly, localized elevated temperatures up to hundreds of degrees Centigrade can instantaneously destroy unwanted tissue, whether malignant or not.
Various surgical devices have been suggested to take advantage of the therapeutic effects of heat applied within the body. These include closed systems containing heated fluid circulated through expandable chambers or catheters adapted for placement proximate to or directly inside target tissue in a surgical site. However, these systems are subject to certain disadvantages and/or operating difficulties.
U.S. Pat. No. 5,545,195 (Lennox et al.) teaches a surgical instrument for interstitial heating of tissue. A sharp distal end of the instrument permits the instrument to be inserted into a solid mass within the body. An expandable chamber is then positioned in the insertion point and expanded within the tissue by the introduction of fluid into the chamber. A heating device located within the expandable chamber heats the fluid as the fluid fills the chamber. A disadvantage of this instrument (for which there is no teaching of the required temperature or clinical end-point for it to be effective) is that the size and shape of the expandable chamber itself impedes the application of heat to difficult to reach anatomic areas. Another serious disadvantage of this instrument is that it must be inserted into the tissue mass. This can be difficult to accomplish depending upon the type of tissue, its anatomic location, vascularity, etc. If the mass can be reached, the sharp distal end may cause bleeding which can obscure the surgeon's view of the surgical site. In addition, the expansion of the chamber within the mass may cause ripping or tearing of tissue. In the worst case, trauma caused by the insertion of the instrument may bring about the spread of malignant cells from the solid mass. The sharp distal end may also inadvertently cause damage to tissue in sites other than the surgical site--a serious concern in endoscopic procedures. Indeed, in certain cases, use of sharp instruments are contraindicated due to the risk of puncturing vital structures.
Other devices employing heated fluids contained in expandable chambers or catheters include the devices disclosed in U.S. Pat. No. 4,949,718 (Neuwirth) for treatment of uterine endometrium; U.S. Pat. No. 4,955,377 (Lennox et al.) for use within blood vessels during balloon angioplasty; U.S. Pat. No. 5,195,965 (Shantha) for treatment of viral infections and cancers; and U.S. Pat. No. 5,540,679 (Fram et al.) for ablation of conduction pathways in the heart. These devices, however, are subject to some or all of the disadvantages described above. Furthermore, no indications are given in the above-identified references regarding the required temperatures or clinical end-point for these devices to be effective.
U.S. Pat. No. 4,160,455 (Law et al.) teaches incorporating a heating element within a container or catheter positioned inside a body cavity. A pump causes fluid to be drawn from the body cavity into the container holding the heating element. At least some of the fluid is heated and expelled into the body cavity. A serious disadvantage of this device (for which there is no teaching of the required temperature or clinical end-point for it to be effective) resides in the heating element being introduced into the body cavity within the cylindrical container at the distal end of the device. Because the container houses the heating element, multiple thermistors, and other elements required to provide heated fluid, the cylindrical container is larger than the connecting pipe. The size of the container limits its ability to access tissue within the body. After insertion into the body, the container may inadvertently and undesirably contact adjacent tissue. The size of the container also limits the volume of fluid to be heated and the flow rate of fluid expelled. Furthermore, using heated body fluid gives rise to the added limitation of fouling the heater with coagulated proteins and the like.
In the medical arts, the application of warmed fluid directly on tissue (rather than in a closed container placed against the tissue) has historically been limited to bathing the integument at temperatures generally below 50.degree. C. The use of hotter fluid has been limited to surgical procedures where filling an entire anatomical site with fluid having a temperature in excess of 50.degree. C. would not cause excessive harm. For example, super-heated water and steam have been applied in the uterus in the treatment of uterine bleeding. This treatment has been abandoned by the medical profession largely because of the problem of uncontrolled burning. Electro-surgical treatments, laser surgical treatments, and, to a large degree, treatments employing heated fluid in closed systems have since replaced this treatment. However, as with the treatments involving contained heated fluid, electro-surgery and laser surgery are not free from disadvantages.
High-frequency current from an electro-surgical unit (ESU), is widely used to cut tissue and coagulate bleeding vessels. Heat is generated by conduction of the electrical current through the tissue. Tissue temperature during electro-surgery can be as high as 800.degree. C. to 1000.degree. C. A limitation of the ESU is that the electrical current may travel through paths of least resistance to damage vital structures which are not the focus of the surgical procedure. Additionally, the current may stimulate nerves and muscles resulting in unwanted twitching or movement of tissue during surgery. These hazards limit the use of the ESU with respect to applications near vital structures. For example, surgeons are generally loathe to use the ESU for surgical procedures within the nasal sinus, particularly near the eye or at the base of the skull. Another limitation is arcing between an ESU electrode and surrounding tissue. Arcing perforates tissue. Thus, use of an ESU for lung surgery is contraindicated.
Lasers are commonly-employed devices for elevating tissue temperature. Absorption of optical radiation by tissue causes the tissue temperature to rise. When delivered appropriately, tissue temperatures may be increased from a few degrees, for shrinkage of collagen for example, to 800.degree. C. to 1200.degree. C. for incisional surgery or wide area ablation. Unfortunately, lasers and the requisite fiber optic delivery devices are very expensive and difficult to use. They often have special power and water requirements. They require special training in their use. They also require the implementation of special safety devices and measures (e.g., protective eye wear, signs on operating theater doors warning prospective entrants of the presence of laser light). Furthermore, like the ESU and the known heated fluid devices, lasers require additional specially-trained operating personnel (i.e., nurses, technicians, or other medical assistants) to adjust the device intraoperatively. Beyond these economic and convenience issues, lasers have other limitations. For example, lasers that operate at a wavelength appropriate to heat target tissue may also operate at a wavelength that scatters energy into non-target anatomical structures causing harm thereto. Another limitation is that beam duration must be monitored with the utmost care. If the laser is not shut off immediately after vaporizing the target tissue, the beam will continue in a straight line, vaporizing or coagulating healthy tissue. This hazard is particularly acute when operating on tissue overlying vital anatomical structures.
Lasers have been used in conjunction with probes that contact tissue. Infrared absorbing materials have been placed on the distal end of a fiber optic device to concentrate the power density toward the end of the contact element and to convert some or all the optical energy into heat. The heat, either alone or in combination with the light, affects the tissue. The combination of heat and laser radiation is used in the treatment of soft tissue in and around the oral and nasal cavities. Contact laser approaches are limited by the same economic and convenience issues as described above in connection with conventional lasers. In addition, the delivery systems used for this type of surgery are quite fragile and are easily damaged. Probe damage is a serious concern, as high power optical energy is often being surgically applied around the eye and brain.
There is a need, therefore, for a surgical instrument suitable for endoscopic applications that, in the hands of a surgeon, is capable of precisely and safely delivering a controlled flow of heated fluid directly to target tissue in the surgical site, and that is free from the disadvantages and adverse effects associated with the known surgical devices identified above.